Well, possibly CE (or more likely ET) at that price. CE seems to be from £529.
CW, I've looked at has been £3k.
My last flights in WT+ ex-EU were a 1/4 of the CW price from the UK (not worth the premium even with double TPs).

People may have villas, property etc. Be renting a car rather than hotels (£400+ to AGP for example).
Then again, maybe they're just booking cheap 80 to 160TP (long) weekends away.

There may be a load of (partial or) non-UK citizens who have status or are able to take advantage of a porentially cheaper starting point? Probably not for the double TP promo, but cheaper fares connecting to JFK etc.